Piezoelectric ceramic compositions

ABSTRACT

PIEZOELECTRIC CERAMIC COMPOSITIONS HAVING VERY HIGH MECHANICAL QUALITY FACTORS AND ELECTROMECHANICAL COUPLING COEFFICENTS AND HIGH STABILITIES IN RESONANT FREQUENCY AND MECHANICAL QUALITY FACTOR OVER A WIDE TEMPERATURE RANGE COMPRISING THE SOLID SOLUTIONS OF   PB(CU1/4NB3/4)O3-PBTIO3-PBZRO3   DEFINED BY THE LINES CONNECTING POINTS A, B, C, D AND E AND THE LINES CONNECTING F, G, H, I, J AND K OF THE DIAGRAM OF FIG. 2 AND FURTHER CONTAINING FROM 0.1 TO 3 WEIGHT PERCENT OF MNO2.

March 14, 1972 MASAMITSU'NISHIDA ErAL 3,649,540

PIEZOELECTRIC CERAMIC COMPOSITIONS Filed Sept. 5, 1969 FIG.I

PbZ r0 FIG.2

INVENTORS MASAMITSU NISHIDA H IROMU OUCHI BY MM ATTORNEYS United States Patent O 3,649,540 PIEZOELECTRIC CERAMIC COMPOSITIONS Masamitsu Nishida, Osaka-shi, and Hiromu Ouchi, Toyonaka-shi, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Osaka, Japan Filed Sept. 5, 1969, Ser. No. 855,575 Claims priority, application Japan, Oct. 1, 1968, 43/ 72,062 The portion of the term of the patent subsequent to Sept. 29, 1987, has been disclaimed Int. Cl. C04b 35/46, 35/48 US. Cl. 252-623 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to piezoelectric ceramic compositions and articles of manufacture fabricated therefrom. More particularly, the invention pertains to novel ferroelectric ceramics which are polycrystalline aggregates of certain constituents. These piezoelectric compositions are sintered into ceramics by ordinary ceramic techniques and thereafter the ceramics are polarized by applying a D-C voltage between electrodes to impart thereto electromechanical transducing properties similar to the well known piezoelectric effect. The invention also encompasses the calcined intermediate product of raw ingredients and the articles of manufacture such as electromechanical transducers fabricated from the sintered ceramic.

The use of piezoelectric materials in various transducer applications in the production, measurement and sensing of sound, shock, vibration, pressure, etc. have increased greatly in recent years. Both crystal and ceramic types of transducers have been widely used. But, because of their potentially lower cost and ease of use in the fabrication of ceramics of various shapes and sizes and their greater durability at high temperatures and/or high humidities than that of crystalline substances such as Rochelle salt, etc., piezoelectric ceramic materials have recently come into prominent use in various transducer applications.

The piezoelectric characteristics required of ceramics apparently vary depending upon the intended application. For example, electromechanical transducers such as phonograph pick-up and microphone elements require piezoelectric ceramics characterized by a substantially high electromechanical coupling coeflicient and dielectric constant. On the other hand, in the ceramic filter and piezoelectric transformer applications of piezoelectric ceramics it is desirable that the materials exhibit a higher value of mechanical quality factor and a high electromechanical coupling coefficient. Furthermore, ceramic materials require a high stability in resonant frequency and in other electrical properties over wide temperature and time ranges.

As a promising ceramic for these applications, lead titanate-lead zirconate has been in wide use up to now. However, it is difiicult to get a very high mechanical quality factor along with a high planar coupling coeflicient in the conventional lead titanate-lead zirconate ceramics. Moreover, the dielectric and piezoelectric properties of the lead titanate-lead zirconate ceramics vary greatly de- 3,649,540 Patented Mar. 14, 1972 ice pending upon the firing technique employed due to the evaporation of PbO.

SUMMARY OF THE INVENTION It is, therefore, the fundamental object of the present invention to provide novel and improved piezoelectric ceramic materials which overcome the problems outlined above. A more specific object of the invention is to provide improved polycrystalline ceramics characterized by very high mechanical quality factors along with high piezoelectric coupling coefficients.

Another object of the invention is the provision of novel piezoelectric ceramics characterized by very high mechanical quality factors, high electromechanical coupling coefiicients, and high stabilities in resonant frequency and mechanical quality factor over wide temperature and time ranges.

A further object of the invention is the provision of novel piezoelectric ceramic compositions, certain properties of which can be varied to suit various applications.

A still further object of the invention is the provision of improved electromechanical transducers utilizing, as the active elements, electrostatically polarized bodies composed of these novel ceramic compositions.

These objects are achieved by providing ceramic bodies which exist basically in the solid solution comprising the ternary system Pb(Cu Nb )O -PbTiO -PbZrO modified with from 0.1 to 3 weight percent of MnO additive.

DESCRIPTION OF THE DRAWING These objects of the invention and the manner of their attainment will be readily apparent from the following description and from the accompanying drawing in which:

FIG. 1 is a cross-sectional view of an electromechanical transducer embodying the present invention.

FIG. 2 is a triangular compositional diagram of mate rials utilized in the present invention.

Before proceeding with a detailed description of the piezoelectric materials contemplated by the invention, their application in electromechanical transducers will be described with reference to FIG. 1 of the drawings wherein reference character 7 designates, as a whole, an electromechanical transducer having, as its active element, a preferably disc-shaped body 1 of piezoelectric ceramic materials according to the present invention.

Body 1 is electrostatically polarized, in a manner hereinafter set forth, and is provided with a pair of electrodes 2 and 3, applied in a suitable manner, on two opposed surfaces thereof. Wire leads 5 and 6 are attached conductively to the electrodes 2 and 3 respectively by means of solder 4. When the ceramic is subjected to shock, vibration or other mechanical stress, an electrical output generated from the ceramic disc can be detected from wire leads 5 and 6. Conversely, as with other piezoelectric transducers, the application of an electrical voltage to electrodes 5 and 6 will result in the mechanical deformation of the ceramic body 1. It is to be understood that the term, electromechanical transducer, as used herein is taken in its broadest sense and includes piezoelectric filters, piezoelectric transformers, frequency control devices, and the like. Moreover, the invention may also be used in and adapted to various other applications requiring materials having dielectric, piezoelectric and/ or electrostrictive properties.

According to the present invention, the ceramic body 1 (FIG. 1) is formed of novel piezoelectric compositions which are polycrystalline ceramics composed of Pb Oll Nb3 4) Oa-PbTIOg-PDZI'Os modified with MnO additive.

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the discovery that within certain particular compositional ranges of this sys tern the specimens modified with MnO additive exhibit very high mechanical quality factors and high electromechanical coupling coefficients along with high stabilities in resonant frequency and mechanical quality factor with distilled water. In milling the mixture care should be exercised to avoid contamination thereof due to wear of the milling ball or stones. This may be avoided by varying the proportions of the starting materials to compensate for (Q over wide temperature and time ranges. 5 any contamination.

The ceramic compositions of the present invention have Following the wet milling, the mixture is dried and various advantages in the processes for their manufacture In X d to insure as homogeneous a IniXtul'e as Possibleand in their application for ceramic transducers. It has the mixture is suitably formed into desired been known that the evaporation of PbO during firing is forms at a pressure of 400 l g./cm. The compacts are a problem encountered in the sintering of lead compounds then pre-reacted by calcination at a temperature of about such as lead titanate-zirconate. The compositions of the 850 C. for about 2hours. invention evidence a smaller amount of evaporated PbO After calcination, the reacted material is allowed to cool than the usual lead titanate zirconates upon firing. The and is then wet milled to a small particle size. MnO ternary system can be fired in the absence of a PhD atmosadditive may be added to the reacted material after calphere. A well sintered body according to the present comcination of raw materials which did not include MnO position is obtained by firing the above described compoand then the reacted material with MnO additive is milled sitions in a ceramic crucible covered with a ceramic cover to a small particle size. Once again, care should be exermade of A1 0 ceramics. A high sintered density is decised as above to avoid contamination by wear of the sirable for resistance to humidity and high piezoelectric milling balls or stones. Depending on preference and the response when the sintered body is utilized as a resonator shapes desired the material may be formed into a mix and for other applications. or slip suitable for pressing, slip casting, or extruding, as

All possible compositions coming within the ternary the case may be, in accordance with conventional ceramic system Pb(Cu Nb )O -PbTiO -PbZrO are represented forming procedures. The samples for which data are given by the triangular diagram constituting FIG. 2 of the drawher-einbelow were prepared by mixing 100 grams of the ings. Some compositions represented by the diagram, howmilled pre-sintered mixture with 5 cc. of distilled water. ever, do not exhibit high piezoelectricity, and many are The mix was then pressed into discs of 8 mm. diameter electromechanically active only to a slight degree. The and 1 mm. thickness at a pressure of 700 kg./cm. The present invention is concerned only with those basic compressed discs were fired at 11604260 C. for 45 minutes positions exhibiting piezoelectric response of appreciable of heating period. According to the present invention, there magnitude. As a matter of convenience, the planar couis no need to fire the composition in an atmosphere of pling coefiicient (K,,) of test discs will be taken as a PhD. Moreover, there is no need to maintain a special measure of piezoelectric activity. Thus, within the area temperature gradient in the firing furnace as is necessary bounded by lines connecting points A, B, C, D, and E in prior art procedures. Thus, according to the present of the diagram of FIG. 2, all compositions polarized and invention, uniform and excellent piezoelectric ceramic tested showed a planar coupling coefficient of approxiproducts can be easily obtained simply by covering the mately 0.2 or higher. The basic compositions in the area Samples with an alumina crucible during firing. of the diagram of FIG. 2 bounded by lines connecting The sintered ceramics were polished on both surfaces points F, G, H, I, I and K, exhibit a planar coupling to the thickness of 0.5 millimeter. The polished disc surcoefficient of approximately 0.5 or higher. The molar faces were then coated with silver paint and fired to form percentages of the three components of compositions A, B, silver electrodes. Finally, the discs were polarized while C, D, E, F, G, H, L] andKare as follows: immersed in a bath of silicone oil at 100 C. A voltage gradient of D-C 4 kv. per mm. was maintained for one gggglggt PbTiOa PbZrOa ipitrlmilense. dlSCS field cooled to room temperature in The piezoelectric and dielectric properties of the polar- 12.5 75.0 12.5

L0 9 30 ized specimen were measured at 20 C. 111 a relative 5g ggg humidity of and at a frequency of 1 kc. Examples 125 4615 4110 of specific ceramic compositions according to this inven- 33 28-8 2% tion and various pertinent electromechanical and dielectric 310 4310 silo 50 properties thereof are given in Table I. From Table I it 3:? gig will be readily evident that all exemplary compositions modified with MnO additive are characterized by very The compositions described herein may be prepared in high mfichanical quality factor a Planar coupling accordance with various well known ceramic procedures. co'efiicleflt an 9 3 are lmlfortant the A preferred method, however, hereinafter more fully 5:; use of piezoelectnc compositions in ceramic filter, piezo- Scribed, contemplates the use of o or pbaob 0120 or electnc transformer and ultra-sonic transducer applica- CuO, Nbzofv Tioz, o and o as Starting maten'ah t1ons. It w1ll be ObVlOUS that the compositions modified T Starting i l i lead oxide w o cupl-ic with MnO additive exhibit a remarkable improvement oxide (C110), niobia (Nb O titania (Tio zirconia of mechanical q y factor (QM) as Compared with that (ZrO and MnO all of relatively pure grade (e.g. CF. 60 of basic compositions; i.e., the basic compositions withgrade) are intimately mixed in a rubber-lined ball mill out Mn0 exhibit a Q of approximately 200 or lower.

TABLE I 24 hours after poling MnOz Planar Mole percent of basic addicou- Mechancomposition tive, Dielecpling ical percent trie eoeth quality Example Pb(Cui 4 by constant, cient, factor Number Nba/OO: PbTiOa PbZrOs weight e KD QM 3. o 46. 0 51. 0 0. 5 651 0. 620 s. 0 4s. 0 4s. 0 0. 2 1, 054 0. as 410 c. 0 44. 0 5n. 0 0. s 970 0. 57 1, s50 12. s 43. s 44. u 0. 1 1, 316 0. 62 310 12. s 44. o 43. 5 o. 5 1, 223 0. 5s 1.150 12. 5 44. 0 43. 5 1. 0 93s 0. s5 1, 230 12. 5 44. s 43. 0 3. 0 747 0. 50 790 The basic compositions of the foregoing examples are indicated in the diagram of FIG. 2 by points numbered correspondingly.

From the foregoing Table I, it is apparent that the values of mechanical quality factor, planar coupling coefiicient and dielectric constant can be varied to suit various applications by selecting the base composition and amounts of MnO additive.

From Table II, it will be evident that the piezoelectric ceramics of this invention exhibit a high resonant frequency stability over a wide temperature range and that these ceramics exhibit a high stability in mechanical quality factor (Q over a temperature range of 30 to 110 C.

TABLE II Q -T.C, fr-T.C, percent percent Exainple number:

Q -T.C is the change in mechanical quality factor (Q within the range 30 to 110 C. f,-T.C is the change in resonant frequency (f,) within the range 30 to 110 C.

These properties are important to the use of piezoelectric compositions in piezoelectric transformer and filter applications etc. The term piezoelectric transformer is here employed to describe a passive electrical energy transfer device or transducer employing the piezoelectric properties of the material of which they are constructed to achieve a transformation of voltage, current or impedance. It is desirable in this application of the ceramic that the piezoelectric materials exhibit a high stability in resonant frequency and mechanical quality factors over a wide temperature range and exhibit very high mechanical quality factors and high electromechanical coupling coefiicients in order that the piezoelectric transformer utilized in a TV set etc. exhibits a high stability with temperature in output voltage and current.

According to the present invention, the piezoelectric ceramics have high electromechanical coupling coeflicients. Therefore, the ceramics of the invention are also suitable for use in electromechanical transducer elements such as phonograph pickups, microphones and voltage generators in ignition systems.

In ceramic compositions containing MnO additive in amounts more than 3 weight percent, the mechanical quality factor is relatively low and the planar coupling coefiicient is low. Ceramic compositions containing an amount of MnO additive less than 0.1 weight percent exhibit a low mechanical quality factor. For these reasons they are excluded from the scope of the present invention.

In addition to the superior properties shown above, compositions according to the present invention yield ceramics of good physical quality and which polarize well. It will be understood from the foregoing that the ternary solid solution (C111 4Nb3 4)OyPbTiOyPbZl'Oa modified with the specified amounts of MnO; additive form excellent piezoelectric ceramic bodies.

While there have been described what at present are believed to be the preferred embodiments of this invention, it will be obvious that various changes and modifications can be made therein without departing from the invention. It is our intention, therefore, to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A piezoelectric ceramic composition consisting essentially of a solid solution of a material selected from the area bounded by lines connecting points A, B, C, D and E of the diagram of FIG. 2, and further containing a quantity of manganese equivalent to from 0.1 to 3 weight percent of manganese oxide (MnO wherein the compositions of the points A, B, D, C and B have the following formulae:

2. A piezoelectric ceramic composition consisting essentially of a solid solution of a material selected from the area bounded by lines connecting points F, G, H, I, I and K of the diagram of FIG. 2, and further containing a quantity of manganese equivalent to from 0.1 to 3 weight percent of manganese oxide (MnO wherein the compositions of the points F, G, H, I, J and K have the following formulae:

3. An electromechanical transducer element comprising a ceramic composition as claimed in claim 2.

4. A piezoelectric transformer comprising a ceramic composition as claimed in claim 2.

5. A piezoelectric ceramic material consisting essentially of the solid solution having the following formula: Pb(CI1 4Nb 4) Ti0 44 ZI'o 4 5O and further containing 0.5 weight percent of manganese oxide (MnO- References Cited UNITED STATES PATENTS 3,268,453 8/1966 Ouchi et a1. 252-629 JAMES E. POER, Primary Examiner I. COOPER, Assistant Examiner US. Cl. X.R. 106-39 R 

